Refrigeration



' July 1, 1941'.

D. G. SMELLIE REFRIGERATION Filed Sept. 20, 1957 2 sheds-sheet 2 Donald G. Smel lz'e ATTORN EY Patented July. 1, 1 941 UNITED 4 REFRIGERATION Donald G. Smellie, Canton, Ohio, assignor to The Hoover Company, North Canton, Ohio, a corporation of Ohio 1 Application September 20, 1937-, Serial No. mass 19 Claims.-

Devices which automatically defrost evaporators of refrigerating. systems are known to the prior art, but prior devices have failed to respond accurately to the frost deposition on the evaporator for the reason that heat radiation between the evaporator and the thermal responsive device has rendered accurate calibration of the apparatus practically impossible. Furthermore, in prior devices the defrosting device has been set to respond to the temperature produced when a predetermined frost depth occurred on the evaporator with the result that they were likely to cause resumption of refrigeration before the frost had melted completely or to fail to respond accurately to a defrosting temperature at the evaporator.

I propose to overcome the above noted defects of the prior art by providing a thermally responsive automatic defrosting cut-ofi for a refrigerating system which is brought into a condition of unstable thermal equilibrium with the evaporator frost coat prior to the attainment of a predetermined depth of frost deposition and is rapid- It is a further object of this invention to provide an automatic defrosting mechanism which simultaneously controls a plurality of energy input devices of different character.

- It is a further object of this invention to provide a positively acting, fully automatic defrosting mechanism which will entirely shut down a continuous absorption refrigerating system of the type utilizing a gas burner to heat the generator and an electric motor to circulate an inert pressure equalizing medium. l

Itis another object of this invention to provide Other and further objects will be apparent as vthe description proceeds when taken in conly actuated by greatly overbalancing the heat transfer between the frost coat and. the thermal. control as soon as the frost coat reaches a predetermined depth.

A thermal device can be made to respond accurately to a predetermined depth of frost by causing a direct heat transfer between the frost coat and the thermal device not quite sumoient to cause the thermal device to actuate the control prior to the deposition of the predetermined depth of frost whereby a slight increase in frost depth will cause a large and rapid withdrawal of heat from the thermal device and rapid actuation of the defrosting control. I attain this resuit by providing a plurality-of projecting heat conductors on the thermal device whichare arranged. to be frozen into the frost coat successively whereby the shortest of the projections will be only very slightly warmer than the frost coat as the frost coat approaches it. This prevents the frost coat from cupping around the shortest of the projections before contact therewith whereby the depth of frost coat at the point of contact with the shortest of the projections is substantially equal to that on other portions of the evaporator. Thus the control is actuated in response to the prevailing depth of frost coat rather than to a. local relatively shallow frost coat.

It is an object of this invention to provide a defrosting mechanism which is fully automatic in operation and which positively responds exactly to a predetermined frost depth on an evaporator.

nection with the accompanying drawings in which: 3

Figure 1 is a diagrammatic illustration of a continuous three-fluid absorption refrigerating system and of the defrosting mechanism with which this invention is particularly concerned.

.Figure 2 is a detail illustration of the defrosting mechanism.

Referring now to the drawings and first to Figure 1 thereof it will be seen that there is illustrated a continuous three-fluid refrigerating system comprising a generator B, a rectifier R, a

- condenser C, an evaporator E, an absorber A, and an inert gas circulating fan F driven by a motor G. These elements are connected by various conduits to form a continuous three fluid absorption refrigerating system including a plurality of liquid and gas circuits.

Refrigerant vapor such as ammonia is liberated in the generator .8 from an ammonia water solution by the application of heat to'the generator. The liberated vapor is conducted to the condenser C through a conduit H containing the rectifier R. Entrainedwater vapor is condensed in the rectifier R and returned through the conduit II to .the generator 13. The refrigerant Weak absorption liquid is conducted from the generator B to the upper end of the absorber A by way of a conduit 13. Strong liquor discharges through a conduit ll connecting the lower end of the absorber A and-a solution reservoir i5. The strong liquor is conveyed from the reservoir through a conduit It in heat exchange relationship with the conduit l3, as indicated, into an analyzing column [1 generator. I

The refrigerant liquid discharges from the confrom which it flows into the duit l2 into the top portion of the evaporator E whereby it may flow therethrough by gravity. A pressure equalizing medium, such as nitrogen or hydrogen, is discharged from the fan F through a conduit I8 into the lower end of the evaporator E whereby it travels through the evaporator in counterflow to the liquid refrigerant. The liquid refrigerant evaporates into the pressure equilizing medium to produce refrigeration in a manner well known in the art, and the mixture of vaporous refrigerant and pressure equalizing medium is conducted. from the evaporator E to the lower end of the absorber A through a conduit l3 which is in heat exchange relation with the conduit 18 previously described. The pressure equalizing medium refrigerant vapor mixture passes upwardly through the absorber in counterflow to the absorption liquid whereby the refrigerant vapor is absorbed in the absorption solution. The pressure equalizing medium exits from the absorber A to the suction inlet of the fan F through a conduit 20. In order to elevate the weak absorption solution. supplied to the conduit I3 to the level of the absorber A, a conduit 2| conducts inert gas under pressure from the conduit l8 into the conduit i3 below the level of the solution in the generator B and analyzer I1,

whereby the weak solution in the conduiti3 is elevated by gas-lift action. I

The generator B is heated by a gas burner 22 of any desired construction. burner 22 is provided with a means for completely shutting oil the fuel supply thereto in the event of complete flame failure. Gas is supplied to the burner 22 from a supplyconduit 23, a normally open defrosting valve 24, a conduit 24'; an adjustable normal control mechanism 25, and a conduit 25. The mechanism 25 may be of any desired character; however it is preferred that'it shall be of the type which is responsive to box or evaporator temperature and is adjustable by means of the movable knob 26. An example of such a mechanism is disclosed in the copending application of Curtis C. Coons, Serial No. 148,424 I with an expansible fluid.

During normal operation the mechanism 25 functions simultaneously to energize the motor G and to provide for a full flame on the burner Preferably the nism is mounted on one wall of the casing 32, preferably .the rear wall whereby this mechanism is not within view from the front of the box. An

insulating frame 33 is suitably secured to a pair of spaced brackets 34 by means of screws 35. The brackets 34 spacethe frame 33 from the wall of the evaporator casing 32 to which the said brackets are secured in any suitable manner.

A bellows housing 36 is rigidly mounted upon the supporting frame 33. An expansible bellows 31 is rigidly mounted on the closure plate 38 of the housing 36. The bellows 31 is filled with any suitable fluid which will change in volume in response to temperature changes. The bellows is provided with three plugs 39, and 4! which project through suitable openings in the closure plate 38 and the supporting bridge 33. The plug 39 is the longest of the three and is relatively small in diameter. The plug 40 is shorter than the plug 39 but of greater diameter. The-plug 4| is the shortestof the three and has the greatest diameter. That is, the cross sectional areas of the plugs are inversely proportional-to their lengths. The plugs may be hollow or solid as desired; if the plugs are hollow they are open to the interior of the bellows and contain the expansible fluids with which the bellows is charged.

The free end of the bellows 31 is provided with an actuating shaft 42 which is slidably journalled in a bushing 43 rigidly attached to the housing 36. The outer end of the shaft 42 is slidably journalled in a bushing 44 which is rigidly carried by a bracket 45 to be more fully described hereinafter.

The bracket 45 comprises a substantially L- shaped member; one arm of the L indicated at 46 extends parallel to the bracket member 33 and spaced therefrom. The other arm of the L 22 in response to a demand for refrigeration.

When the evaporator reaches the temperature for which knob 26 is set, the mechanism 25 deenergizes the motor G and causes theflame on the burner 22 to be decreased to a mere igniting or pilot flame.

Referring now to Figure 2, the defrosting mechanism will be described in detail. The

evaporator is provided with a casing 32 which preferably entirely surrounds the cooling coils. with the exception of the box cooling coil, and the ice freezing trays. The defrosting mechaindicated at 41 extends substantiallyat right angles to the bridge'element 33 and is attached thereto by means of a pair of spaced laterally projecting tongues 38, only one of which is shown. The tongues 48 are secured to the bridge 33 by means of screws 43. The bushing 44 is mounted in the arm 46 of the bracket member.

The arm 46 of the bracket." receives the power supply lines 29 and. 3| through an insulat ing grommet 46'. These wires are connected to a pair of spaced contacts indicated generally at 50 which are carried by the bracket arm 43 in any suitable manner. A bridging contact is indicated at 5] and is carried upon one arm 52 of a snap mechanism to be described hereinafter.

The bridging contact Si is suitably insulated from the arm 52.

The arm 52 together with a toggle arm 54 and a spring 55 form the active elements of a well knownform of over-center toggle mechanism. The arms 52 and 54 are provided with forked bearing arms 52' and 54', respectively, which engage in grooves formed in the outer ends of a pair of forked arms 51 integrally formed with a the reduced portion 53 and on the other byengagement with a flxed collar 60 on the shaft 42.

' face 82.

The arrangement just described is such that longitudinal'movement of the shaft 42 is transmitted ,to the arm 84 whereby the bridging contact 5| is caused to move from open to closed, or closed to open position with a snap action.

The outer end-of the arm 52 abuts a fixed stop 6| on the bracket arm 41 when it is in open circuit position.

The gas. supply control mechanism will now be'described. The gas valve 24 comprises a valve chest 62 and a cap plate 68 which are rigidly secured together and to the arm 41 of the bracket 45 by means of nuts and bolts 64 and 85. The

valve chest and cap plate are separated by means I of a washer 88 and a flexible diaphragm 81 which are engaged therebetween. Gas is supplied to the interior of the valve chest 62 through the conduit 23, previously described, and a gas conduit 88. Gas exits from the valve chest .62 by way of a valve port 68, a passageway 18, gas passage 1|, and the conduit 24' previously described.

A suitable pilot by-pass is indicated at 12 and is controlled by an adjustable valve 13. I

The valve port 68 is controlled by a valve plug 18 which is rigidly mounted upon a valve shaft 15. The shaft 15 extends through the valve plug 14 and is received in a journal 16 formed integrally with the valve chest 62 and projecting intothe passage 18. The valve plug 14 is urged to open position by a spring 11 which is positioned in the passageway 18.

The flexible diaphragm 61 is rigidly attached to the shaft 15 in a gas-tight manner, as indicated at 18, by any suitable means.

The cap plate 63 is provided with an elongated journal 18 which receives the outer enlarged portion 88 of the'shaft 15. The journal 18 projects through a suitable opening in the arm 41 of the bracket 45. i

The actuating mechanism for the gas valve will now be described. The outer end of the enlargement 88 abuts the central portion of a small leaf cushion spring 8| which is rigidly at-- tached to the bight portion of a channel-shaped bell crank actuating arm 82. The arm 82 is pivotally mounted upon a pin 88 which is rigidly .held in a pair of spaced'ears 84, only one of -means of a stiff spring 81 which abuts a collar 88 rigidly mounted on the shaft 42. The collar 88 and spring 81 normally act as a rigid connection; their principal function is to prevent lost motion 'between the actuating shaft 42 and the bell crank 82.

Thus it will be seen that translatory movement of the actuating shaft 42 is imparted to the valve plug 14 through the medium of a bell crank 82 and the valve plug shaft 15-88.

A lock-out mechanism is also provided 'and' will now be described. A bi-metallic thermostat 88 is rigidly mounted on the side of the bridge 88 adjacent the evaporator casing 32 by means of screws 88. The free end of the bi-metallic thermostat 88 carries a latch keeper 84 which is provided with a tapered face 8| and a latching Clockwise movement, as viewed in Figure 2, of the bi-metallie .thermostat 88 is limited by means of a stop 88 formed integrally with the arm 41 of the bracket 48.

The arrangement is such that counterclockwise movement of the bell crank 82, as viewed in Flgure'2', will move the valve plug 14 to closed position, the switch bridging contact 5| to open circuit position, and will cause-the free end of the bell crank 82 to ride over the inclined surface 8| and to latch behind the surface 82 on the latch keeper 84.

The operation of this invention will now be described. During normal operation the defrosting mechanism is inoperative and has no eflect upon the apparatus. The machine is cycled by the control mechanism to produce refrigeration in the normal manner in accordance .with

the setting of the knob 28. After a considerable period of normal operation, frost will begin to freeze plug 48 whereupon the frost will again the last freeze plug 4|.

the frost coat on the evaporator.

cup around the plug 48 for a small depth and will then freeze in that plug. Under these conditions there is a condition of thermal balance, namely, a transfer of heat from the air in the box through the bellows 31, the freeze plugs 38 and 48, and the frost to the evaporator. The apparatus is so designed that this heat transfer is insufficient to cause collapse of the bellows or to cause the freeze plugs 38 and 48 to melt free of Continued normal operation of the apparatus will cause continual frost deposition until the frost approaches There will .be no cupping of the frost around the plug 4| for the reason that the excellent heat transfer between the frost and the frozen-in plugs 88 and 48 will prevent any substantial heat radiation to the ,ice by the plug 4|; therefore, the plug 4| will be directly contacted by the outer surface of the frost. The rate of heat transfer from the fluid within the expansible bellows 81 through the freeze plugs 38, 48 and 4| will greatly exceed the rate of heat transfer from the air in the box to the bellows 31 as soon as the plug 4| is frozen in with the result that the bellows collapses.

Collapse of the bellows will move the shaft 82 inwardly toward the evaporator with the result that the bridging'contact 8| is snapped away from the contact 88 and-the inert gas circulating fan is rendered inoperative. Inward movement 82 latches behind the latch keeper 84 on the bimetallic thermostat 88 shortly after the valve port 88 is closed. A slight over-riding of the bell crank 82 is permitted by the leaf spring 8|. The

apparatus is now entirely inoperative'regardless of the action of the normal control mechanism 28.

The apparatus remains in latched position until the frost melts from the evaporator. Obviously the bellows 21' willqbegin to expand long before the frost is completely removed from the plugs 39, ill and I.

fact that the bell crank a: is latched in position by the thermostat 89. When the frost is entirely meltedfrom the evaporator casing 32 the temperature of that casing rises above 32 degrees Fahrenheit and allows the bi-metallic thermostat CI to warm up. As the bi-metallic thermostat ll warms up it begins to move in a counterclockwise direction, as viewed in Figure 2, and shifts the latch keeper 94 out of the path of the bell crank lever 82 whereupon the apparatus returns to normal operation.

The iii-metallic thermostat 89 is mounted on the bridge 33 facing the evaporator whereby it is affected by the temperature of the frost coat on the casing 32. The thermostat flexes in a clockwise direction wheneverthe temperature of the. casing 32 falls below the melting point of ice. As a result of this design the mechanism is always in condition to lock the refrigerating system out of operation whenever the frost deposition reaches a predetermined depth upon the evaporator casing.

It will be seen from the above that I have devised an automatic defrosting mechanism which isresponsiv'e in a very accurate manner to a predetermined frostdeposition upon the evaporator casing and which also simultaneously operates to shut off the gas supply to the gas burner and the supply of energy to the electric drive motor.

Another novel feature of my invention resides in the fact that both the Sylphon bellows 31 and the bi-metallic strip 89 are responsive to a differential of temperature. The insulating bridge 33 prevents direct heat radiation from the Sylphon 31 to the evaporator 32 with the result that the heat flow'must all occur through the freezing The bi-metallic thermostat 8! is exposed on one face to radiation to and from the wall of the evaporator casing and on the other face to the air within the refrigerating compartment.

In operation, the Sylphon bellows 31 assumes a substantially static condition until such time as the heat flow therelnto from the air in the box is over-balanced by the heat flow from the bellows to the frost coat on the evaporator whereupon it collapses very rapidly. These factors make for very accurate control and insure that the apparahis will positively render the refrigerating system inoperative in responseto a predetermined depth of frost coat upon the evaporator casing.

While I have illustrated and described only one form of my invention, it is to be understood that this is to .be taken as illustrative only and not in a limiting sense. Various changes may be made in the form and arrangement of parts 'without departing from the spirit of the invention orthe scope of the appended claims.

I claim: .1. In a refrigerating system having a heat exchange portion subject to ice deposition, means responsive to a. predetermined ice deposition for rendering said system inoperative, said means comprising a thermal element ands heat transfer means in heat transfer relationship-with said thermal element positioned to be contacted by a frost coat forming on said heat exchange Portion, said heat transfer means increasing in total heat conductivity in a direction away from said heat exchange portionand means responsaid system from resuming operation until said heat exchange portion is ice free.

2. Defrosting apparatus comprising temperature responsive means, heat transfer means for governing the thermal condition of said temperature responsive means and in heat transfer .relationship therewith comprising a, plurality of projecting heat conducting elements of varying lengths arranged so that the longest element has the smallest heat conductivity, 2. control mechanism, means operated by'said temperature responsive means adapted to operate said control mechanism, and temperature responsive means locking said control means in operated position.

,3. In a refrigerating system having an evaporator, means for supplying energy to said system, means to control the supply of energy to said system, a supporting member on said evaporator and in spaced relation thereto, a temperature responsive expansible bellows carried by said supporting member, heat conducting plugs in heat exchange relation with said bellows projecting through openings in said support toward said evaporator but spaced therefrom, a shaft carried by said bellows, means interconnecting said shaft and said energy supply control means to' cause interruption of said energy supply when said plugs are frozen into ice deposited on said evaporator, a thermostat mounted on said support positioned to respond to the temperature" of the surface of said evaporator, a member on said interconnecting means movable adjacent said thermostat, means on said thermostat positioned to allow movement of said memher to energy supply interrupting position and to restrain return movement until the surface of said evaporator is above the melting point of frost.

4. Absorption refrigerating apparatus comprising a generator, a, condenser, an evaporator, and an absorber connected in circuit to form a continuous three-fluid refrigerating system, power-driven means connected in said circuit to circulate a pressure equalizing medium through the evaporator and absorber, heating means positioned to heat said generator, means normally controlling said apparatus between predetermined temperature. limits, means for rendering said power-driven means and said heating means inoperative whenever a predetermined depth of frost occurs on said evaporator comprising a thermostatic element having a critical operating thermal condition, and heat transfer means thermally connected to said thermostatic element and arranged to lower the temperature of said thermostatic element to the critical value in response to the formation of an exactly presaid temperature responsive means and said energy supply control means, ,a r id heat conducting means thermally bonded to said temperature responsive means comprising a plurality of projecting' heat conducting elements adapted to be successively frozen into a frost deposit.

sive to a condition of said system for preventing v5 6. 'Ihat method of insuring accurate response of athermal device to a frost coating on an evaporator which comprises the steps of forming a direct heat conducting path between said thermal element and said frost coat, and progressive- 1y increasing the area of said path and shortenreached a predetermined thickness.

7. The method of rendering a thermally redition 'of said evaporator operative torelease said latching means.

sponsive medium responsive to a predetermined .thickness of material normally progressively.

built up which comprises placing the thermally responsive medium in an atmosphere having a temperature different from that of the material,

forming a direct heat conducting path between said material and thethe'rmally responsive me-' dium as the material builds up; and progr s ively increasing the area of said path while decreasing its length until the rate of heat transfer between the thermally responsive medium and the material is, greater than the rate of heat transfer between the thermally responsive medium and the atmosphere. 7 a 4 8. Defrosting mechanism comprising means for controlling the supply of energy to a refrigerator, means responsive to a predetermined thickness of frost operative to cause said energy supply control means to discontinue supply of energy, comprising a thermostatic element, a plurality of heat conducting elements of different lengths projecting from said thermostatic element, the longer heat conducting elements having a smaller cross sectional area than the shorter elements and temperature responsive means for locking said energy supply control means in position to prevent energy supply until said frost is melted.

9. Refrigerating apparatus comprising an evaporator, energy consuming means for supplying liquid refrigerant to the evaporator, means means comprising means adapted to bring said frost depth responsive means 'into thermal equilibrium with the frost coat on said evaporator prior to the accumulation of frost thereon ."11. In combination, a refrigerating system .including an evaporator, means for supplying energy to operate said system, a thermal responsive device mounted adjacent 'to but in spaced relationship with said evaporator,.,insulating' means preventing heat radiation'between said evaporator and said thermally responsive device, and means adapted to form a direct heat conducting path between material forming on the surface of said evaporator and said-thermally responsive device, and means interconnecting said energy supply control means and said ther-' mal' responsive device.

12. Defrosting mechanism comprising a gas supply valve, an electric switch, "means responsive to a predetermined immersion in frost and operative upon such immersion to close said valve and open said switch, means operative to look said valve in closed position and said switch in open position, and means operative to release said locking means when subjected to an effective temperature above 32 F.

13. Defrosting mechanism comprising a ther- 'mal bellows mounted on a heat insulating support, a plurality of heat conducting elements of different lengths projecting through said support, the length of said heat conducting elements being inversely proportional to the cross-sec- V tional area thereof whereby said thermal device is operated with great rapidity when all of said heat conducting elements are contacted by a cold body.

14. In a device of the character described, a

temperature responsive element, heat conducting means in heat exchange relation with said temperature responsive element and projecting therefrom, the cross-sectional area of said heat conducting means decreasing progressively in a direction away from said temperature responsive element.

to the above mentioned predetermined depth,

means. for quickly overbalancing said thermal equilibrium between said frost coat and said frost depth responsive means when the frost coat reaches the above' mentioned predetermined depth, and means responsive to a defrosted condition of the evaporator for causing resumption of energy supply.

10. In combination, an evaporator, a gas supply valve, an electric switch, a temperature responsive bellows adapted to collapse when subjected to the temperature of a frost coat on said evaporator, heat :conducting means connected to said bellows and positioned to be frozen into a frost coat forming on the surface of said evaporator to lower the temperature of said bellows very close to the temperature of said frost coat,

and other heat conducting means connected to said bellows and adapted to lower the temperature of the bellows to that of the frost coat rapidly when the frost coat reaches a predetermined depth, means operated by collapsing movement of said bellows for opening said switch, means operated by collapsing movement of said bellows for closing said valve, latching means moved 15. In combination, an article subject to frost deposition, 9. defrosting control mechanism including a frost depth responsive thermostat positioned adjacent said article, heat conducting means arranged to provide a heat conducting path between said article and thermostat of insuflicient capacity to operate said thermostat, .and other heat conducting means arranged to provide a heat conducting path of large capacity between said thermostat and said article when the frost depositing on said article reaches a predetermined depth.

16. In combination, an article subject to frost deposition, 9. defrosting control mechanism including a frost depth responsive thermostat positioned adjacent said article, means for bringing said thermostat to the temperature of the frost'coat on said article comprising a plurality of heat conducting elements in heat transfer relationship with said thermostat terminating at varying distances from the surface of said article, the arrangement of said heat conducting elements being such that they are progressively frozen into the frost coat forming on said article to progressively lower the temperature of said thermal element and the heat conducting eleme-:ts not yet contacted by the frost coat substantially to the temperature of the frost coat whereby the thermostat will be actuated rapidly when the frost coat contacts the shortest of the .heat conducting element and therewill be no tendency for the frost coat tocup around said shortest heat conducting element prior tact therebetween.

17. That method of insuring accurate response of a thermal element to the thickness of a body to conwhich increases in thickness by accretion which 8 includes the steps of providing a heat conducting path between the body and the thermal element before the body reaches a predetermined 'depth, such heat conducting paths being sufli- .cient to bring about a condition of thermal equilibrium between the body and the thermal element, and providing an additional heat conducting path between the body and the thermal element when the mined depth. 1

18. Refrigerating apparatus comprising a cooling unit, means for supplying a cooling medium to said cooling unit, means for governing the operation of said coolingmedium supply means in response to a predetermined condition of said cooling unit, means tending to bring said governing means into thermal equilibrium with'said cooling unit prior to the attainment of such body reaches such predeter-.

predetermined condition, and means for overbalancing such thermal equilibrium quickly in a given direction upon the attainment of such predetermined condition by said cooling unit.

19. Refrigerating apparatus comprising a cooling unit, means for supplying a cooling medium to said cooling unit,- means for governing the operation of said cooling medium supply means in response to apredetermined condition of said cooling unit, means tending to bring said governing means into thermal equilibrium with said cooling unit prior to the attainment or such predetermined condition, means for overbaiancing such thermal equilibrium quickly in a given direction upon the attainment of such predetermined condition by said cooling unit, means for 

